Neural circuits are assembled from a group of neurons via specific synaptic connections, and are the functional and structural units of the nervous system. Abnormal neural circuit and synaptic function lead to many types of neurological disorders. We are interested in mapping the functional components of neural circuits, dissecting the synaptic mechanisms by which the circuits process information, and understanding how genes regulate this process and how this ultimately produces and reshapes behavioral output. Given the immense complexity of the human nervous system and its inaccessibility to genetic manipulation, genetic model organisms with a relatively simple nervous system, such as C. elegans and Drosophila, have been widely used to investigate these questions. C. elegans has recently emerged as an increasingly popular genetic model for studying various phenomena in neurobiology, due to its simple and well characterized nervous system and amenability to genetic manipulation. Notably, C. elegans represents the only organism whose connectome (wiring diagram of its entire nervous system) is known. Additionally, many basic principles governing neural signaling, processing and development are conserved in C. elegans. About two-third of human disease genes have homologs in this organism. However, it remains largely enigmatic how the C. elegans nervous system is functionally organized to generate behaviors. We have recently developed an automated calcium imaging system that allows recording of neural activity in freely-behaving animals. We have also developed a multidisciplinary approach to map the neural circuits underlying behavior by integrating functional imaging, optogenetic interrogation, genetic manipulation, laser ablation, and electrophysiology. Using this approach, we will map the functional components of motor circuits, investigate the synaptic mechanisms by which the circuits process information, and characterize how sensory cues regulate the circuit dynamics to modulate behavioral output. As the microcircuits and the synaptic mechanisms employed by worms to process information show striking similarities to those by mammals, our study will provide novel insights into the neural basis of behavior in higher organisms.